Magnesium primary cell



Aprll 3, 1 951 A. B. FRY ET AL MAGNESIUM PRIMARY CELL Filed Jan. 27,1949 1N VEN TORS. /Ls/ra/B. Fry

Roy C. Kirk Per@ E Geo/ye M( A TTOR/VEY Patented Apr. 3, 1951 2,547,9o7MAGNESIM PRIMARY cani.

Ashford B. FryyRoy C. Kirk, and'Percy F. George,

-' Midland,` Mich.,v assignors -tollhe "Dow Che'nic'al Company, Midland,Mich., 'a coi-poration'f Delaware l*Application-January 27, 194B, SerialNo.

(Cl. 13G-100) l 22 Claims. 'Iloeinvention relates to an improvediprimarycell.

One oftheobjects of the invention is topro- Vide a primary4 cellutilizing as the anodematerial, more electively thanheretofore,.magnesium and itsalloys. Anotherzobject. is.to providey aprimary celllhaving4 ahigh capacity and voltage, coupledywitha longshelf` life. `Still.otherolojects and advantages` will become, apparentVfrom the followingV descriptionof the invention.

The essential Velements of the` new .primarycell are briefly: a metallicanode of magnesium.or magnesium-base alloy in lWhich the -magnesiumcontent exceeds 'about 50 `percent kand. Apreferably exceeds about A80`per cent of the ialloy by Weight; an aqueous` electrolyte comprising abromidecf an alkali -or alkaline earth metal, the electrolyteadvantageously "containing, .corrosion-inhibiting amounts of a chromicacidsaltof a base consisting of an -alkalinmetalbasa an :alkaline earthmetal base including magnesium, and ammonium; and a ,cathode of achemically inert, electrically conducting material such as carbonorjgraphite in combinationwth a ,depolarizer of manganese dioxide.

The three essential elements of the ycellare arranged in a suitablemanner to provide a voltaic system in which the-anode is separated from`the cathode and the electrolyte provides a path for the passage ofelectrical current between them as in.- conventional cell construction.

THEv ANODE AReferring more particularly `tothe elements of the cell,4the anode, We have found',.may be-made of magnesium itself, althoughbetter cellsareobtained with ourcombin'ation of elements whenmagnesium-base. alloys: are used, particularly those in which thealloy-ing; constituents are aluminum, zincand'manganeser as inthe usualstructural magnesium-base alloys.. Forlowestc'orrosionrates of theanode, magnesium or alloy of the highest purity grade is? to: be used,ihav-ing no more than traces of the impurities Fe, CuandNi, whichpromote-corrosion of the metal. While impuritiesin the magnesium affect.the shelf life. vol"V the cells theyv donotseriously limit..tl`1ecapacity of the cells or their Vuseful life. on continuousgpr many kindsof intermittent, serlVice..Tl1'e-usual commercial grades of magnesium.are generally.l satisfactory for anode material,especiallypwhen' theiron content does not exceed about 0.002 per cent and that of nickel0.001 'per cent. The term magnesium as hereinafter' employed includesnot only magnesium, either in the pure or in the impure form, but alsothe magnesium alloys in which magnesium is the predominant constituent.

The following tabulation setsI forth examples of magnesiumebase alloyswhich are suitable for anode material and their corresponding A. S. T.M. designations.

TABLE I Anode composzzons Nominal Composition l A1185' A. S. T. M.Designation v A Al ,Mn Zn vZr Cc 1. A3" 3 0.2 2'. A4-; 4 0.2 8.y ,-AS..V8 0.1 4- y A10 10 0.1 5 A12. l2 0.1 6; 2. 0.3 7. 3 0.2 8.--.- 6; 0.29m.- 6 0.2 l0 8. 0. 2y 11 9 f' 0.2 1,2. V 9 V0.1 13,. 14. 2 l5. l 2vv16,. M 1.5 17 2 1.y f v. 19. 20L-.. Z1.-

1 Balance commercial magnesium.

The anode material mayheinany of the usual forms such as rolled plateorsheet, extrusions, forgings, stampings, and castings.

THE ELECTROLYTE The electrolyte--may be prepared by dissolving thebromide salt' infwaterin` a' concentration betWee'nfA about 30 grams per.liter and that producing a nearly saturated solution at ordinarytemperatures. The actual concentration used doesAV not appeartobe-critical-,I althoughU :for best results certainconcentiationsare-to be preferred depending upon the particular bromide or com#bination of...bromide's used. For-' etample, preferred-.concentrationsofthe alkalimetalbromides areifrornaboutV 1.5"()I to41 500y grains-ofthesalt-per literf of solution.A 01% theal-lali-{metal ldr-ftliiides;vlithium bromide producs the Iiiostdes'iablelfesults, particularly` iniconcentrations of abouti-300 grams per liter. Similar concentrations maybe used with the alkaline earth metal bromides. As used herein, the termalkaline earth metal bromide includes the bromides of Mg, Ca, Ba, andSr. Of these, magnesium bromide is to be preferred. Its most erl'ectiveconcentration is about 300 grams per liter of solution.

While a single bromide may be used as the electrolyte, We have foundthat still better results are had with combinations of the aforesaidbromides, particularly combinations of an alkali metal bromide with analkaline earth metal bromide, these results being manifest in greatershelf life and higher capacity than that exhibited by single bromideelectrolytes. For example, We have found that an electrolyte containingmagnesium bromide in combination With any one of the otheraforementioned bromides or ammonium bromide produces an improved cell.Particularly advantageous as a mixed bromide electrolyte is thecombination of magnesmm bromide and lithium bromide. A somewhat moreeconomical cell results when sodium bromide is substituted for thelithium bromide.

It is desirable to include in the electrolyte an alkali metal, alkalineearth metal (including magnesium), or ammonium salt of chromic acid incorrosion-inhibiting amounts, such as from 0.01 gram per liter ofsolution to concentrations producing saturation in the presence of thebromide therein. A preferred concentration of the chromic acid salt is0.05 to 2 grams per liter of solution.

THE CATHODE The cathode comprises an inert conductor such as a piece ofcarbon or graphite to which a terminal may be alxed, if desired, and adepolarizer of manganese dioxide having in admixture therewith fromabout 5 to 25 per cent by weight of finely divided carbon such as carbonblack. Acetylene black is preferred and may be used in a proportion ofabout 5 per cent to 15 per l cent and preferably about 10 per cent byweight.

In preparing the cathode depolarizing mixture, it is desirable first tomix the manganese dioxide depolarizer with the nely divided carbon so asto obtain uniform distribution of the carbon black throughout themanganese dioxide, which is also pulverulent. Thereafter the mixture maybe moistened with electrolyte so as to obtain a moldable mixture, aswhen the mixture is to be molded into a dry cell bobbin. Suitableproportions of electrolyte and dry cathode mixture are about 36 c. c. ofelectrolyte per 100 grams of mixture, although other proportions may beused.

CELL ASSEMBLY lCells of either the Wet or dry type may be assembled invarious ways employing the three elements above described. Probably themost commercially valuable application of the invention lies in the drycell eld Where the instant cell has the advantage of high capacity andvoltage coup-led with lightness in weight. In compounding a cell of thedry cell type according to the invention the anode may take the form ofthe vessel in which the other two elements of the combination arecontained and the electrolyte may be thickened or jellied as inconventional dry cell practice by the inclusion therein of a thickeningagent such as cereal flour or starch or a mixture of them in theproportions of about 1 gram of thickening agent per 6 c. c. ofelectrolyte solution. In cells of this type the cathode is formed into abobbin as by molding the manganese dioxide-carbon black mixture around acentral electrode of carbon, the whole being moistened with electrolytebefore introducing the bobbin into the cup which constitutes the anode.In assembling the combination of the dry cell elements it is convenientto place in the cup or can a quantity of the electrolyte solution mixedwith the thickening agent and suitable insulation to keep the bobbinfrom coming into direct contact with the anode before inserting thebobbin.

The invention may be further explained and illustrated with reference tothe accompanying drawing in which Fig. 1 shows a cutaway isometric Viewof a wet cell;

Fig. 2 shows a vertical section of a dry cell.

The cell illustrated in Fig. 1 is contained in a container or jar I ofsuitable insulating material such as glass, hard rubber or plastic,which is divided into an anode compartment 2 and a cathode compartment 3by means of a partition 4. Partition 4 consists of a board or plate ofsuitable insulating material which is conveniently made of moldedphenol-formaldehyde resin. It is provided With a plurality ofperforations 5 arranged in a regular pattern, to permit passage ofcurrent through the electrolyte between the electrodes. On the .cathodeside of the partition 4 is a porous lter medium 6, such as a sheet oflter paper, which serves as a liquid-permeable retainer for the contentsof the cathode. In compartment 2 is disposed an anode I consisting of aplate of magnesium or alloy thereof in which magnesium is thepredominant constituent. To the anode is secured a terminal rod 8, theanode being immersed in a body of the liquid electrolyte 9 alreadydescribed. Cathode Il] is disposed in compartment 3 and is provided witha terminal wire II.

vThe cathode I0 is embedded in a mass I2 of a depolarizer mix composedof powdered manganese dioxide and finely divided carbon, e. g. carbonblack or acetylene black moistened With the electrolyte.

The cell of Fig. 2, which is of the dry cell type, is contained in theVessel or cup I3. The vessel I3 serves as the anode and is formed ofmagnesium or alloy thereof in Which the magnesium is the predominantconstituent. The upper edge of the Vessel may be provided With aterminal or binding post Ill. Arranged inside the container andprojecting above it is the carbon or graphite electrode I5 which may beprovided with a terminal or binding post I6. Associated with theelectrode I5 is the depolarizing mixture I'I of manganese dioxide andcarbon black which may be molded or pressed into a cake around theelectrode and, together with the electrode, forms a bobbin I8. Thebobbin I8 preferably is more or less saturated with the aqueouselectrolyte, already described, before inserting the same into thevessel I3, The bobbin I8 ts inside the vessel, leaving a space I9between the outside of the bobbin and the inside of the vessel which islled with gelled electrolyte. The bobbin I8 is prevented from touchingthe vessel by the insulating bushing 20 and washer 2| at the lower endof the vessel and by the washer 22 and sealing compound 23 at the upperend of the vessel. In some instances, if desired, the space I 9 may belled with a porous insulating material such as blotting paper soakedWith electrolyte.

The following examples, tabulated in Table II, are illustrative of wetcells made up in accordance with the invention.

TABLE II Wet cells Cathode Electrolyte 1 Dlgleer A d A er Per ...et 'NQ-rial 2 1 v01 Grams i per Liter Salt M1102 A. B.

1U 20 10 10 10 8.5 10 8. 0 3. 0 25 2. 5 .4. o 8 O dO l0 8.0 9Sr'BrLHzO-i- 10 8.0

MgBr2.6H20.

1 Volume of electrolyte per cell 300 c. c. l '2 Rolled plate 3.5" x 2" X0.25. 'Iron content 0.002%; nickel content 0.00l%.

2In'the tabulation above, the electrolytes ofthe cells Vare aqueoussolutions containing the vbrotlxamples Qf; :dry cells `embodying thelinvenf; Ation are tabulated in Table III. These cells are of the saineconstruction as that illustrated 4in Fig. .2, and conform vin `size toconventionalD size dry cells. The cathode material is a mix.- ture of 90parts of manganese dioxide and 410 parts by `Weight of Vacetylene black.moistened with electrolyte of the vcomposition set forth in the table.Cells numbered 1 to 21 inclusive contain single bromide electrolytes,While cells nurnbered 22 to 27 inclusive contain mixtures of theaforesaid bromides.

The capacity data set `forth in `the last three columns of Table IIIVare based upon tests described in the bulletin No. JAN-BL-lSA entitledJoint Army and Navy Specication Batteries Dry, published-by the UnitedStates Government October 7,1947. In.the'BA-8 tests the cells weredischarged through a resistance of 331/3 ohms continuously untilthe cellvoltage dropped to 1.13 volts. The number ofhours of such .dischargingis set forth inthe column headed 13A-8. In the TABLE III Dry cellsElectrolyte, Grams per Liter H Capac'vy-Ao rs., Cell No. Anode Material1 BA 8 Salt Inhibitor Initial 3 Months 1 300 LBI 423 23. 0 2 dn 385 22.6 3 do 449 21.0 4 dn 409 22.8 f5 300 MgBlzlHeO 473 23. 8 A6 do .499 33.3 7 do one 24. 6 g8 dn 5 (N H4)2Or04 20. 3 l) do 10 Na2ClO4 3 47 23.6 dnio Mgoro., 361 24. o 300 CaBr2.2H2O 10 (N H4 2Cr04 4495 25.3 300 KBr 5(NH4)2CrO4 10.1 1000 SrBrzHzC 0.2 (NH4)2CIO4 142 l0. 2 do do 152 9.0 16810. 5 148 l1. 8 147 11. 0 9. 4 1o (NHmCrO4 10.3 0.1. CaCrQ4 20. 0 9. 124. 2 ,22. 2 18. 2 19. 3 100 MgBrz.6H2O-i200 KBI. 17. 5 100MgBlz.GH20--200 SI`B12.6H20. d 20. 9

1 Fe content less than 0.002%; Ni content less than 0.001%.

Inides already set forth,v and the anodes are formed of themagnesium-base alloy Whose composition corresponds to the A. S. T. M.designation given in TableI, and the cathodes are depolarized withmanganese dioxide in admixture with acetylene black (designated: A. B.)in the proportions shown. The elements of the cells are arranged as inFig. l, the cell container having inside dimensions of 3.25 inches long,2.63 inches Wide, and 3.5 inches deep.

In testing the performance of these cells each of them was dischargedthrough an adjustable resistance set at a value which produced a cur-:rent density on one face of the anode of 6 amperes per square foot atthe commencement `of the discharge. Thus each cell was started todischarge at the same current density per unit vof anode area, and thedischarge was continued u ntil the voltage at the `terminals of thecells While discharging was 1 volt. The resulting energy output duringthe discharge was computed ampere hours and set forthin the last col,-:uxnn of theV table.

BA-30 tests the -cells were discharged through a resistance of 6% ohmsfor four minutesv every 1/2 hour for 10 hours each day 5 days per Weekuntil the cell voltage dropped to 0.935 vvolt. In thecolumn headedInitial there are set forth the number of days of discharging accordingto the BA-30 schedule, the discharging commencing as soon as themanufacture of the cells was ccmpleted. In the last columnl the BA-30discharge test Was commenced after the cells had been held in storagefor 3 months on open circuit' at about F. Data was not obtained Whereblanks exist in the capacity columns.

From Table III it is evident that cells in which the electrolytecontains magnesium bromide either alone or in combination With an alkalimetal bromide exhibit exceptional capacity both for continuous as Wellas for intermittent service. Particularly advantageous are cells inwhich the anode material is a magnesium-base alloy of the AZ type, ormoreparticularly magnesium alloys containing about 2 to 9 per cent ofaluminum, 0.5 to 3 per cent of zinc, 0,1 .to 0.5 per cent of manganese,the balance being commercial magnesium in which the impurities iron andnickel preferably do not exceed about 0.002 and 0.001 per centrespectively, and the electrolyte is magnesium bromide in combinationwith lithium bro mide. Long service cells are also obtained whenammonium bromide is used in the electrolyte along with either the alkalior alkaline earth metal bromide. In such instances the ammonium bromidemay be used in a concentration of about 10U-275 grams per liter ofsolution. A preferred concentration is about 150 grams of ammoniumbromide per liter in combination with one of the other bromidesaforementioned.

As aforementioned, we have found that it is desirable to include in theelectrolyte a chromic acid salt of an alkali metal, an alkaline earthmetal, or ammonium in corrosion-inhibiting concentrations such as 0.01to 5 grams per liter of solution in order to reduce the open circuitcorrosion and improve the uniformity of the closed circuit corrosion ofthe anode material, and a number of cells made up in this way are shownin Table III. Similar results are obtained with other chromic acid saltsof the kind aforementioned such as Li2CrO4. However, the presence of oneof the above mentioned chromic acid salts in the electrolyte sometimeshas the disadvantage of causing a delay in the cells attaining a workingvoltage following a rest period after a use of the cell. The delay is,We have found, a function of the concentration of the inhibitor, asshown by the data in Table IV.

TABLE IV D size dry cells Grams per Seconds' Delay iter before Cell(NHmCrOl Attains l Volt Eleetrolytez300 g. p. 1. MgBrgHgO.

Anode AZ31, iron less than 0.002%, nickel less than 0.001%.

Cathode: 90% MnOz-l-l0% acetylene black.

We have discovered that the voltage attain- TABLE V Per Cent Cal-Seconds Delay cium in Anode before Cell Metal Attains l Volt 0 (Blank)5. 3

Electrolyte: 300 g. p. l. MgBrzHzO; 5 g. p. l. (NHzCrOl.

In the foregoing table each delay reading is the average of two cells,and each cell was first discharged through a 5-ohm resistor for 1 hour,then rested for 17 hours before measuring the delay. After the restperiod the average time in seconds required for the cells to attain 1volt at the terminals on again being discharged through the 5-ohmresistor was recorded and set forth in the table above as the delay.Each cell employed a manganese dioxide-depolarized cathode formed of amixture of parts of manganese dioxide and 10 parts by weight ofacetylene black.

In order to achieve a desirable control of anode corrosion in the cell,and at the same time avoid adverse effects on the time of attainment ofoperating voltage following a rest period after use, we have found thatthe concentration of the inhibitor should preferably not exceed about 2grams per liter unless the anode metal contains calcium as aforesaid, inwhich case as much as 5 grams per liter may be used. Thus the presenceof calcium in th eanode alloy is a distinct advantage, not only from thestandpoint of reducing the delay in voltage attainment but also inpermitting longer useful cell life before the anode wall becomesperforated due to corrosion by the electrolyte while at least partiallyovercoming the increased delay in voltage attainment occasioned by thepresence of the inhibitor in the electrolyte.

Similar advantages are had as regards controlling delay in voltageattainment after a rest period following a use of the cell with cellscompounded with mixed electrolytes. In Table VI delay data are set forthfor examples of D size dry cells using mixed bromide electrolytes andanodes of AZ31 to which was added 0.15% of calcium. The electrolytescontained 1.0 gram per liter of ammonium chromate as inhiibtor.

A characteristic of all the foregoing cells is their initial relativelyhigh voltage of about 1.9 to 2.0 volts. Inasmuch as this high voltagedoes not persist for long on using the cell it is generally advantageousto short circuit each new cell for a short time, such as about 1.5minutes, before use. This has the effect of lowering the cell voltage toa stable value of about 1.65 to 1.70 volts, which may be considered thenominal voltage of the cell. A similar effect as regards this reductionof the initial voltage of the cell to its nominal voltage may be had byrendering the electrolyte alkaline by adding to it a small amount of analkali such as ammonia instead of short circuiting the cell.

In operation, cells made according to the invention constitute a uniquevoltaic system inasmuch as the cathode is depolarized by manganesevdioxide operating in an alkaline medium. Attempts heretofore to usemanganese dioxide as a depolarizer in an aqueous alkaline medium havebeen unsuccessful. For example,` the zinc Le 9 Clanch cell becomesuseless vwhen the electrolyte becomes alkaline, due to the resultinglarge .drop .in Voltage of the cell. In contra-distinction .to this, inoperation the electrolyte of our cells exhibits a pH of a least about8.5, a pI-I at which conventional cells employing a manganesedioXide-depolarized Thus the present cells make it possible to utilizeeiectively not only magnesium and its alloys as anodic material but alsomanganese dioxide in an alkaline -voltaic system. v

While the magnesium in the anode may be usual commercial quality whichcontains small amounts of some other elements as impurities, it ispreferable to employ magnesium which does not contain more thanabout0.005% of iron and 0.002% of nickel, if any. 'Ihus the .anode maybe'formed of either pure magnesium or of a magnesium-base alloycontaining a major portion. of the metal, all such materials being-included with the term magnesium hereinafter employed.

It is to be understood that the foregoing description is illustrati-Verather than strictly limitative, and that other embodiments of the newcell are possible within the spirit of the invention Yand the scope ofthe following claims.

We claim:

1. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of an inorganic bromide selected from the groupconsisting of the bromides of the alkali and alkaline earth metals.

2. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of an inorganic bromide selected from the groupconsisting of the bromides of the alkali and alkaline earth metals, saidaqueous solution containing corrosioninhibiting amounts of a chromicacid salt of a base selected from the group consisting of the hydroxideof an alkali metal, alkaline earth metal, and ammonium.

3. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution containing the bromide of an alkali metal and thebromide of an alkaline earth metal.

4. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution containing the bromide lof an alkali metal and thebromide of an alkaline earth metal, said aqueous solution containingcorrosion-inhibiting amounts of a chromic acid salt of a base selectedfrom the group consisting of the hydroxide of an alkali metal, alkalineearth metal, and ammonium.

5. In a primary cell the combination comprising a magnesium' anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of an alkaline earth metal bromide.

6. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of an alkaline earth metal bromide, said aqueoussolution containing corrosion-inhibiting amounts of a chromic acid saltof a base selected from the group consisting of the hydroxide of analkali metal, alkaline earth metal, and ammonium,

cathode do not function..

7. In a primary cell the .combination comprising a magnesium' anode,.apmanganese dioxidedepolarized cathode, and .an'electrol'yte comprisingan aqueous solution containing magnesium bromide. Y

8. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution containing magnesium bromide, said aqueous solutioncontaining corrosion-inhibiting amounts of a chromic acid salt of a baseselected from the group consisting of the hydroxide of an alkali metal,alkaline earth metal, and ammonium.

9. In a primary cell the combination comprising va magnesium anode, aVmanganese dioxidedioXide-depolarized cathode, and an electrolytecomprising an aqueous solu ion containing lithium bromide.

10. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution containing lithium bromide, said aqueous solutioncontaining corrosion-inhibiting amounts of a chromic acid salt of a baseselected from the group -consisting of the hydroxide of an alkali metal,alkaline earth metal, and ammonium.

11. In-a `primary cell the .combinationlcomprising a magnesium anode, .amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of magnesium bromide and lithium bromide.

12. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of magnesium bromide and lithium bromide, said aqueoussolution containing corrosion-inhibiting amounts of a chromic acid saltof a base selected from the group consisting of the hydroxide of analkali metal, a1- kaline earth metal, and ammonium.

i 13. In a primary cell the combination comprising an anode of magnesiumcontaining from 0.05 to 0.5 per cent of calcium, a manganesedioxidedepolarized cathode, and an electrolyte comprising an aqueoussolution of an inorganic bromide selected from the group consisting ofthe bromides of the alkali and alkaline earth metals.

14. In a primary cell the combination comprising an anode of magnesiumcontaining from 0.05 to 0.5 per cent of calcium, a manganesedioxidedepolarized cathode, and an electrolyte comprising an aqueoussolution of an inorganic bromide e selected from the group consisting ofthe bromides of the alkali and alkaline earth metals, said aqueoussolution containing corrosion-inhibiting amounts of a chromic acid saltof a base selected from' the group consisting of the hydroxide of analkali metal, alkaline earth metal, and ammonium.

y15. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of magnesium bromide and ammonium bromide.

16. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of magnesium bromide and ammonium bromide, said aqueoussolution containing corrosion-inhibiting amounts of a chromic acid saltof a base selected from the group consisting of the hyroxide of analkali metal, alkaline earth metal, and ammonium.

17. In a primary cell the combination comprising an anode of amagnesium-base alloy containing about 2 to 9 per cent of aluminum, 0.5to 3 per cent of zinc, 0.1 to 0.5 per cent of manganese, the balancebeing magnesium, a manganese dioxide-depolarized cathode, and anelectrolyte comprising an aqueous solution of magnesium bromide, saidaqueous solution containing corrosion-inhibiting amounts of ammoniumchromate.

18. In a primary cell the combination comprising an anode of amagnesium-base alloy containing about 2 to 9 per cent of aluminum, 0.5to 3 per cent of zinc, 0.1 to 0.5 per cent of manganese, and 0.05 to 0.5per cent of calcium, the balance being magnesium, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of magnesium bromide.

19. In a primary cell the combination comprising an anode of amagnesium-base allow containing about 2 to 9 per cent of aluminum, 0.5to 3 per cent of zinc, 0.1 to 0.5 per cent of manganese, and 0.05 to 0.5per cent of calcium, the balance being magnesium, a manganesedioxidedepolarized cathode, and an electrolyte comprising an aqueoussolution of magnesium bromide, said aqueous solution containingcorrosion-inhibiting amounts of a chromic acid salt of a base selectedfrom the group consisting of the hydroxide of an alkali metal, alkalineearth metal, and ammonium.

20. In a primary cell the combination comprising an anode of amagnesium-base alloy containing about 2 to 9 per cent of aluminum, 0.5

to 3 per cent of zinc, 0.1 to 0.5 per cent of manganese, 0.05 to 0.5 percent calcium, the balance being magnesium, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of magnesium bromide and strontium bromide, said aqueoussolution containing corrosion-inhibiting amounts of ammonium chromate.

21. In a primary cell the combination comprising a magnesium anode, amanganese dioxidedepolarized cathode, an an electrolyte comprising anaqueous solution containing calcium bromide.

22. In a primary cell the combination comprising a magnesium anode, amanganese dioxide-depolarized cathode, and an electrolyte comprising anaqueous solution containing calcium bromide, said aqueous solutioncontaining corrosion-inhibiting amounts of a chromic acid salt of a baseselected from the group consisting the hydroxide of an alkali metal,alkaline earth metal, and ammonium.

ASHFORD B. FRY. ROY C. KIRK. PERCY F. GEORGE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,343,194 Lawson Feb. 29, 19442,445,306 Lawson July 13, 1948

1. IN A PRIMARY CELL THE COMBINATION COMPRISING A MAGNESIUM ANODE, AMANGANESE DIOXIDEDEPOLARIZED CATHODE, AND AN ELECTROLYTE COMPRISING ANAQUEOUS SOLUTION OF AN INORGANIC BROMIDE SELECTED FROM THE GROUPCONSISTING OF THE BROMIDES OF THE ALKALI AND ALKALINE EARTH METALS.